Processes for hydroformylating an olefin to prepare a carbonyl derivate containing one carbon atom more than the starting olefin by reacting the olefin with carbon monoxide and hydrogen, which mixture is also called synthesis gas, in the presence of a Group VIII metal, e.g., rhodium, in complex combination with an organic ligand and carbon monoxide also being a component of the catalyst complex, are well known in the art (referred to sometimes as “OXO” processes) and have enormous industrial importance. The hydroformylation of olefins can be conducted in mode of the “liquid recycle process” where the product is recovered in liquid form, see U.S. Pat. No. 4,148,830 or in the process mode of the “gas recycle process” according to U.S. Pat. No. 4,593,127. According to the gas recycle process mode, synthesis gas and olefin are sparged through the liquid reaction mixture and the gas stream taken from the hydroformylation reaction zone contains the desired aldehydes in addition to unreacted olefin and synthesis gas. Because substantial amounts of the unreacted olefins are dissolved in the product streams taken from the hydroformylation reactor, the art discloses several techniques to recover said valuable olefin and to recycle it to the main hydroformylation reaction zone and, occasionally, to use it in a vent hydroformylation reaction zone.
According to U.S. Pat. No. 5,367,106 the gaseous effluent vented from the primary process is condensed in a heat exchanger and the uncondensed gas and liquid are separated in a gas-liquid separator. The non-condensed vent gases containing unreacted olefin and synthesis gas from the gas-liquid separator are then introduced into a secondary hydroformylation reactor. It is a characteristic feature of the process of U.S. Pat. No. 5,367,106 that the solubilized rhodium-phosphorus complex catalyst is circulated between said primary and secondary process.
U.S. Pat. No. 5,105,018 likewise discloses a two-stage reactor system in the hydroformylation of olefins. The gaseous reactor effluent is cooled to 70° C. and then subjected to a gas-liquid separator. The gaseous product from the gas-liquid separator is partially returned to the first reactor stage, while the other portion is fed to a second reactor stage, acting as a vent reactor. The liquid formed in the gas-liquid separator after cooling and which contains a substantial amount of unreacted olefin is then subjected to a gas-liquid contact zone, also known in the art as a gas-liquid stripping zone, where the liquid is countercurrently contacted with carbon monoxide and hydrogen in order to strip unreacted olefin from the product. The recovered olefin from this operation is recycled to the first reactor system.
According to U.S. Pat. No. 5,648,553 the gas stream withdrawn from the hydrofromylation reaction zone is cooled to 40° C. and the liquid formed is heated again using a heat exchanger. After adjusting the temperature the liquid is provided to a gas-liquid contact zone in order to recover unreacted olefin from the liquid stream. The separation efficiency of the unreacted olefin can be improved by heating the feed temperature of the liquid feed to the gas-liquid contact zone.
Also noted is Chinese Patent Publication CN 20214826 which discloses a system for separating organic phases in stages in in connection with a hydroformylation reaction.
Thus, the art teaches a one-stage cooling step of the reactor effluent or an additional heating step of heating the cooled liquid process stream obtained down-stream from the gas-liquid separator before entering into gas-liquid contact zone. Significant drawbacks of one-stage cooling is that large amounts of product aldehyde is recycled and/or the product stream contains large amounts of olefin that cannot be efficiently removed in the gas-liquid contact zone. Reheating condensate, on the other hand, adds additional costs for equipment and energy.